【学术视频】第八届国际磁科学会议 | 日本京都大学Tsunehisa Kimura教授

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图 | Tsunehisa Kimura

题   目：Diamagnetism induced by atomic-level eddy current

报告人：Tsunehisa Kimura

单   位：Kyoto University, Japan

时   间：2019-10-13

地   点：中国科学院合肥物质科学研究院

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报告摘要

Langevin (or Larmor) diamagnetism results from an additional motion of bound electrons induced by an applied dc magnetic field. On the other hand, diamagnetism is also observed when an ac magnetic field is applied to free electrons in conducting material. This is due to the eddy current predicted by Faraday's law of induction. Then, a question may arise: does eddy current occur at the atomic level? The answer is "yes" and we call this diamagnetism Faraday diamagnetism.  Figure 1 shows schematic of the motion of a bound electron under dc and ac magnetic fields. 
Fig. 1 Comparison of (a) Faraday diamagnetism under ac magnetic field and (b) Langevin diamagnetism under dc magnetic field. The direction of the force F acting on bound electron is (a) (anti-) parallel to the electric current J, while it is (b) perpendicular to J.

The electric current J of the system (a) induced by the applied ac magnetic field 𝐁̇(𝑡) is described by an RL electric circuit composed of the self-inductance L due to a coil formed by the orbital motion of electron and the resistance R due to thermal noise. Then, the response J and the resultant magnetization M is derived. We obtained the diamagnetic susceptibility 𝛾 for Faraday diamagnetism as follows: 𝛾 = 2𝐾𝜒 

where 𝜒 is the Langevin susceptibility and 𝐾 is Nagaoka constant ( 0 ≤ 𝐾 ≤ 1 ). The total susceptibility measured experimentally is 𝜒 + 𝛾, indicating that diamagnetism is enhanced.

Due to this enhancement, the anisotropic susceptibility ∆𝜒 + ∆𝛾 might also increase under ac magnetic field. We performed magnetic orientation of microcrystals of L-alanine under rotating magnetic fields and obtained a result, ∆𝛾/ ∆𝜒=0.94. This is consistent with the theoretical prediction above. 

个人简介

Prof. Tsunehisa Kimura is a professor at the Kyoto University. Prof. Kimura received his Ph.D. from Kyoto University in 1981. His major interest is magnetic processing of soft materials such as organic materials, polymers, biomaterials, cellulose and carbon materials and so on. He received “The Award of the Society of Polymer Science” in Japan in 2001 based on his outstanding contribution to magneto-science and polymer science. His current research interests include visualization and utilizing the effect of magnetic fields on non-magnetic materials.

会议简介

2019年10月11日-14日，第八届国际磁科学会议在合肥成功举办。本次会议由中国科学院强磁场科学中心、中国科学院强磁场与离子束物理生物学重点实验室和西北工业大学生命学院空间生物实验模拟技术国防重点学科实验室主办，安徽大学物理与材料科学学院协办，并得到了中科院国际合作局的支持。强磁场条件下的科学研究涉及物理学、化学、材料科学、地球科学、生命科学与医学等众多学科。国际磁科学会议是国际上关于磁场下的材料和生命科学研究最有影响力的国际会议之一，吸引了全世界众多专家学者参与。

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